Conductive polymers have been studied for several years now as candidates to partly replace silicon-based electronic systems. An electrochemical transistor engineered using conductive polymers has been disclosed, for example, by Nilsson et al., Adv. Mater. 14, No. 1, 2002, p. 51. Moreover, an electrochemical transistor engineered using conductive polymers has been demonstrated in combination with display elements comprising conductive polymer material by P. Andersson et al., Adv. Mater. 14, No. 20, 2002, 1460.
Electrochemical devices implemented using conductive polymers react more slowly than those electronic devices implemented in silicon. Therefore the electrochemical devices based on conductive polymers seem suited for slow processes taking in the range of seconds, minutes, hours, days, weeks or months.
One example of the use of an electrochemical device made using conductive polymers is a display element. The display element is made from a local chemical cell in which chemical reactions can happen in a time-dependent manner. The chemical reactions could either be chemical or electrochemical in nature, and change the physical state of the apparatus in a way that the change can easily be recognised, for example as a colour change. Such electrochemical display cells are disclosed, for example, in the U.S. Pat. No. 5,930,023 (assigned to Wisconsin Label Corporation). The electrochemical display cells disclosed in this patent are arranged in layer form with two electrode layers and an electrolyte layer occupying distinct areas of a substrate. An electrolyte layer overlaps most of one electrode layer but contacts a smaller portion of the other electrode layer, which is made of a thin film. When activated, an electrochemical reaction progressively increases the area occupied by the thin-film electrode layer and progressively decreases the area occupied by the thin-film electrode layer. The thin-film electrode layer recedes at a boundary in common with the electrolyte layer and provides an irreversible indication of change at a rate governed by the electrochemical reaction. Therefore the Wisconsin Label patent makes use of the change within the display cell. The area available for activation is rather limited, though. Only areas covered by the electrode are accessible for activation. The activation depends on a flowing electrical current.
GB patent application 2 295 241 A assigned to Mino Green discloses an electrochromic display. A variable reflectivity mirror under protective glass comprises: a layer of fluorine-doped tin oxide conductor; an electrochromic transparent layer made of W03, going blue when hydrogen is introduced; a porous layer of SiO2/Al2O3 which becomes moist on exposure to humidity; and a layer of reflective metal e. g. silver, which is porous enough to allow access of water vapour to the porous layer of Si02/Al2O3. The mirror's reflectivity is varied by applying an appropriate potential between the layers of fluorine-doped tin oxide conductor and the layer of reflective metal. The Green application does not disclose a permeability of an at least one activation layer along transversal direction across a surface of the at least one migration layer. The Green application does not disclose an activation of the at least one activation layer being achievable along a direction transversal to the at least one activation layer.
US patent application 2005 / 006 8 603 Al assigned to Berggren et al. discloses an electrochromic device comprising (i) at least one material that is electrically conducting in at least one oxidation state and (ii) at least one elelectrochromic material, wherein said materials (i) and (ii) can be the same or different; at least one layer of solidified electrolyte which is in direct electrical contact with said electrochromic element(s); and at least two electrodes comprising PEDOT-PSS arranged side by a side in common plane and adapted for application of a voltage therebetween. One of the said electrodes is in direct electric contact with a component selected from said electochromic element(s) and the other electrode(s) is in direct electrical contact with a component selected from said electrolyte layer(s) and said elelectrochromic element(s). Furthermore an electrochemically active element is provided which comprises a first layer comprising PEDOT-PSS mixed with an adhesion promoter, and a second layer comprising PANI the second layer being deposited on top of and in direct electrical contact with the first layer.
The Berggrin application requires require application of a voltage between at least two electrodes formed by PEDOT-PSS. Furthermore, the Berggren application does not disclose an activation of the at least one activation layer along a direction transversal to the at least one activation layer.
US patent 5,216,536 assigned to Donnelly Corporation, Holland, Michigan discloses an electrochromic device incorporating a moisture control layer comprised of either water reservoir material or water scavenger material in conjunction with a moisture permeable intermediate barrier layer within the device. The water reservoir material provides a source of water for those electrochromic stacks which require water for proper apparition. For stacks which require protection from moisture, water scavenger material may be utilized. A moisture permeable intermediate barrier layer separates the moisture control layer from the electrochromic stack. The Donnelly system aims at improving an electrochromic element. The Donnelly system does not disclose an activation of an activation layer along a direction transversal to the at least one activation layer.